Golf Club Head and Method of Making Same

ABSTRACT

A golf club head is described which has a body that is formed at least in part from a stainless steel alloy having the following composition in weight percent: 
                                       Carbon   0.25 max.         Manganese   14-20         Silicon   up to 2.0         Phosphorus   0.05 max.         Sulfur    0.5 max.         Chromium   12-22         Nickel    3.5 max.         Molybdenum   0.5-4           Copper    2.0 max.         Nitrogen   0.2-0.8         Boron   0.06 max.                                         
The balance of the alloy is iron and the usual impurities. The stainless steel alloy provides a hardness of about 80 HRB up to about 25 HRC. The golf club head provides a unique combination of high strength and hardness, good ductility, excellent “feel”, and good durability. A method of making the disclosed golf club head is also described.

FIELD OF THE INVENTION

This invention relates to golf club heads and in particular to an iron golf club head made from a corrosion resistant steel alloy that provides a unique combination of strength, ductility, and feel.

BACKGROUND OF THE INVENTION

Golf club manufacturers are continuously on the lookout for new golf club materials which provide better “feel” than materials currently in use. That property is especially desirable in irons and high-lofted clubs such as wedges. It is believed that a major component of the “feel” characteristic of a golf club is the sound and vibration damping characteristics of the metal from which the club head is manufactured. The overall shape and design of the club head also contribute to its feel characteristic.

Another important property for an alloy used in a golf club head is resistance to corrosion. In this regard, steel alloys containing relatively high amounts of chromium and/or molybdenum have been favored. Among the currently used stainless steel materials are AISI Type 431 and Type 304, and precipitation hardenable grades such as 15-5, 17-4, 13-8, and the CUSTOM 450 and CUSTOM 455 stainless alloys. Typically, club heads made from Type 431 and the Type 304 are considered to have better “feel” than club heads made from the precipitation hardenable grades which have much higher strength. The fact that the Type 431 and Type 304 alloys have hardness that is softer than the precipitation hardenable grades, has led to the belief that hardness is inversely proportional to “feel”.

Some corrosion resistant non-ferrous alloys such as copper-beryllium have been used for making golf club heads to provide a “soft feel”. In addition, many of the alloys which are known for good “feel”, such as AISI 8620 and cast iron, are very soft. However, all of these soft alloys have the disadvantage of being so soft that they lack the durability of the harder stainless steel golf club alloys. This lack of durability can be seen in a lack of resistance to scratching and denting, as well as easier movement of the loft and lie angles during normal play.

The loft angle of a golf club is a measure of how far the face of the club is set relative to a line that is perpendicular to the ground. The lie angle is the angle at which the shaft comes off of the club head. In the making of a club, golf club producers often adjust both the loft and lie angles of the golf club head by bending the club head. The softer alloys are more easily adjusted, but their adjustment can change over time from the stresses inflicted on the head during normal play.

In view of the foregoing, it would be desirable to have a golf club head which is made of a corrosion resistant steel alloy that provides good hardness, strength, and ductility, better “feel” relative to the known higher strength golf club heads, and better durability than the known soft club heads.

SUMMARY OF THE INVENTION

In accordance with a first aspect of this invention, an iron golf club head is provided which has a body that is formed at least in part from a stainless steel alloy having the following composition in weight percent:

Carbon 0.25 max. Manganese 14-20 Silicon up to 2.0 Phosphorus 0.05 max. Sulfur  0.5 max. Chromium 12-22 Nickel  3.5 max. Molybdenum 0.5-4   Copper  2.0 max. Nitrogen 0.2-0.8 Boron 0.06 max. The balance of the alloy is iron and the usual impurities. The stainless steel alloy provides a hardness of about 80 HRB up to about 25 HRC where HRB refers to the Rockwell B hardness scale and HRC refers to the Rockwell C hardness scale. The Rockwell B scale ends at 100 HRB whereas the Rockwell C scale begins at 20 HRC.

In accordance with a second aspect of the present invention, there is provided a method of making a golf club head. The method includes the following steps. Charge materials are selected and melted to provide a stainless steel alloy having the following composition in weight percent:

Carbon 0.25 max. Manganese 14-20 Silicon up to 2.0 Phosphorus 0.05 max. Sulfur  0.5 max. Chromium 12-22 Nickel  3.5 max. Molybdenum 0.5-4   Copper  2.0 max. Nitrogen 0.2-0.8 Boron 0.06 max. and the balance is iron and the usual impurities. The alloy is cast into a mold and allowed to solidify into the form a body of a golf club head. The golf club head body is processed to provide a finished golf club head. The golf club head is then heat treated to provide a hardness of about 80 HRB-25 HRC if it does not provide such hardness in the as-cast condition.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is an exploded perspective view of a multi-piece golf club head made in accordance with the present invention.

DETAILED DESCRIPTION

An austenitic stainless steel alloy sold under the registered trademark “15-15LC” was designed for and has been used exclusively for making components for the oil-drilling industry, primarily drill collars. Alloys sold under the mark “15-15LC” are described and claimed in U.S. Pat. No. 3,904,401 and U.S. Pat. No. 5,308,877, both of which are incorporated herein by reference.

The inventors have discovered that the 15-15LC alloy has properties that also make it highly suitable for iron golf club heads. The term “iron” as used herein, refers to the golf clubs known as irons, as opposed to other types of golf clubs referred to as woods and putters. As used herein the term “iron golf club” includes golf clubs known as wedges.

The golf club head according to the present invention departs from the state of the art in iron golf clubs because it is made from an austenitic stainless steel alloy having the following weight percent composition: up to about 0.25% max. carbon; about 14-20% manganese; up to about 2.0% silicon; up to about 0.05% max. phosphorus; up to about 0.5% max. sulfur; about 12-22% chromium; up to about 3.5% max. nickel; about 0.5-4% molybdenum; up to about 2.0% max. copper; 0.2-0.8% nitrogen; and up to about 0.06% max. boron. The balance of the alloy is iron and the usual impurities present in commercial grades of stainless steel alloys. Preferably, the stainless steel alloy comprises the following, in weight percent: up to about 0.15% max. carbon; about 16-18% manganese; up to about 1.0%, better yet, not more than about 0.75% silicon; up to about 0.03% max. phosphorus; not more than about 0.03% max. sulfur; about 16-19% chromium; up to about 2.5% max., better yet, not more than about 1.5% nickel; about 0.75-2.5% molybdenum; up to about 2.0% max. copper; 0.3-0.7%, better yet, about 0.4-0.6% nitrogen; and up to about 0.01% max. boron.

An iron golf club head made in accordance with the present invention has a one-piece design or a multi-piece design. The one-piece embodiment is preferably produced by investment casting or by forging. Examples of multi-piece golf club heads are shown and described in U.S. Pat. Nos. 7,014,571 and 7,207,899, the disclosures of which are incorporated herein by reference.

The cast form is produced by melting charge materials to make the stainless steel alloy described above. The molten alloy is then cast into a ceramic mold having a cavity that defines the basic shape of the golf club head. After the alloy solidifies and cools, the mold is removed to yield a preform of the golf club head.

The forged form of the club head according to this invention is produced by melting the stainless steel alloy and casting it into an ingot. The ingot is hot worked to an intermediate form, preferably bar. The bar is then cut into segments that approximate the size of the golf club head. The bar segments are then hot forged with dies that define the basic shape of the golf club head.

It is also contemplated that a golf club head according to the present invention can be made by powder metallurgy techniques. In such a process the stainless steel alloy described above is melted and then atomized, preferably with nitrogen gas, to form metal powder. The metal powder is filled into a die mold having a cavity that defines the basic shape of the golf club head. The metal powder is then consolidated such as by sintering, hot isostatic pressing, or cold isostatic pressing to form a near net shape of the desired golf club head preform.

In any of the foregoing processes, the golf club head preform is preferably machined to its finished dimensions and shape. The club head is then ground and polished as necessary to provide an aesthetic appearance. The hardness for the golf club application is about 80 HRB to 25 HRC to provide good durability. That level of hardness can be achieved in the as-cast club head because the material may self-anneal. If the desired hardness is not provided in the as-cast condition, then the cast club head can be annealed at about 1900-2100° F. for about one hour. Preferably, the club head is heat treated to a hardness of about 85 to 95 HRB. For certain types of irons where additional hardness and strength is desired, such as in the long or intermediate irons, the as-cast golf club head can be cold worked, such as by cold forging, prior to the finish machining operations. The cold worked club head would then be annealed to achieve its final hardness, preferably about 30 HRC.

In accordance with another embodiment of the golf club head of this invention, as shown in the drawing, there is provided a multi-piece iron club head 10. The multi-piece head 10 includes a body 20 that is preferably made from an austenitic stainless steel alloy such as the 15-15LC alloy described above. The multi-piece head 10 also includes a face plate 30. The face plate 30 is made of a harder material than the body 20. Preferred materials would be a precipitation hardenable stainless steel alloy, titanium, or a titanium alloy. The face plate is attached/bonded to the body by welding, brazing, or by mechanical means, such as press fitting or shrink fitting.

We have found that the large amount of manganese present in this alloy benefits the sound and the dampening characteristics of a club head made from this alloy, as compared to club heads made from other stainless steels which significantly less manganese. In addition to the good hardness, strength, and “feel” provided by the club head according to this invention, the club head according to this invention also has excellent ductility and toughness. The latter two properties are desirable because they permit bending of the hosel, the portion of the club head that connects to the shaft, in order to adjust the loft and lie angles of the club. Since this alloy has higher relative strength than the known “soft” golf club alloys, the loft and lie angles of the club head are less likely to change during normal play.

It will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It is understood, therefore, that the invention is not limited to the particular embodiments that are described, but is intended to cover all modifications and changes within the scope and spirit of the invention as described above and set forth in the appended claims. 

1. A golf club comprising a head that is formed at least in part from a stainless steel alloy having the following composition in weight percent: Carbon 0.25 max. Manganese 14-20 Silicon up to 2.0 Phosphorus 0.05 max. Sulfur  0.5 max. Chromium 12-22 Nickel  3.5 max. Molybdenum 0.5-4   Copper  2.0 max. Nitrogen 0.2-0.8 Boron 0.06 max.

and the balance is iron and the usual impurities; wherein said stainless steel alloy provides a hardness of about 80 HRB to about 25 HRC.
 2. The golf club set forth in claim 1 wherein said head comprises a body and a face plate assembled together and the body is formed of said stainless steel alloy.
 3. The golf club set forth in claim 2 wherein the face plate is formed of a material selected from the group consisting of a precipitation hardenable stainless steel, titanium, and a titanium alloy.
 4. The golf club set forth in claim 1 wherein said head is formed entirely of said stainless steel alloy.
 5. A method of making a golf club head comprising the steps of: melting charge materials selected to provide a stainless steel alloy having the following composition in weight percent: Carbon 0.25 max. Manganese 14-20 Silicon up to 2.0 Phosphorus 0.05 max. Sulfur  0.5 max. Chromium 12-22 Nickel  3.5 max. Molybdenum 0.5-4   Copper  2.0 max. Nitrogen 0.2-0.8 Boron 0.06 max.

and the balance is iron and the usual impurities; casting said stainless steel alloy into a mold; solidifying said stainless steel alloy in said mold to form a body of a golf club head or a preform thereof; and then processing said body to provide a finished golf club head.
 6. The method as set forth in claim 5 wherein the step of processing said body comprises the step of heat treating said golf club head to provide a hardness of about 80 HRB to about 25 HRC.
 7. The method as set forth in claim 5 wherein the step of casting the stainless steel alloy comprises the step of investment casting the stainless steel alloy.
 8. The method as set forth in claim 6 wherein the step of processing the body of said golf club head comprises the step of machining the body to finished dimensions.
 9. The method as set forth in claim 5 wherein the step of processing said body comprises the steps of cold working said body and then heat treating the cold-worked body to provide a hardness of about 30 HRC.
 10. The method as set forth in claim 5 wherein the step of casting the stainless steel alloy comprises the step of casting the alloy into an ingot mold, the step of solidifying the stainless steel alloy comprises the step of forming bar from said alloy, and the step of processing the golf club head body comprises the steps of: forging the bar to provide a semi-finished golf club head; and then machining the semi-finished golf club head to finished dimensions.
 11. The method as set forth in claim 5 comprising the step of bonding a face plate to said golf club head body after said processing step.
 12. The method as set forth in claim 11 comprising the step of forming the face plate from a material selected from the group consisting of a precipitation hardenable stainless steel, titanium, and a titanium alloy. 